1. Field of the Invention
This invention generally relates to a surface acoustic wave device, and more particularly to a surface acoustic wave transducer of high frequency and wide band which is capable of being manufactured easily and to a method for producing the same.
2. Description of the Prior Art
A conventional surface acoustic wave transducer of edge-bonded type is illustrated in FIG. 1. In the figure, 1 is an elastic member, 1' is a surface acoustic wave propagation face or surface, 2 is a piezoelectric member, 3 and 4 are electrodes, 5 is an electric signal input terminal and 6 is a surface acoustic wave.
As illustrated, to propagate the surface acoustic wave 6 on a face 1' of the elastic member 1, a laminated structure comprised of the electrodes 3 and 4 and the piezoelectric member 2 is provided, at an end face of the elastic substrate 1, and extends perpendicular to a propagation direction of the surface acoustic wave to be produced.
As to the dimensions of the piezoelectric member 2, the piezoelectric member 2 has an effective width a and a thickness b. If a wavelength of the surface acoustic wave at a center frequency thereof is assumed to be .lambda..sub.0, a.perspectiveto..lambda..sub.0 and b.perspectiveto.(.lambda..sub.0 /2.
When an AC voltage is applied to the electric signal input terminal 5, the piezoelectric member 2 vibrates. As a result, surface acoustic wave 6 is produced at an end portion of the face 1' of the elastic member 1 and propagated leftwardly as viewed in FIG. 1.
Although this conventional transducer has a wideband characteristic, it is difficult to produce said transducer practically. As methods for producing this transducer, there can be mentioned:
(1) a method in which the piezoelectric member 2 is first formed and electrodes 3 and 4 are provided on opposite ends thereof, respectively, and the resultant assembly is bonded to the end face of the elastic material; and PA1 (2) a method in which the metal electrode 3 is vacuum deposited on the end face of the elastic member 1, the piezoelectric thin film 2 (e.g. zinc oxide etc.) and another metal electrode 4 are vacuum deposited thereon. PA1 an elastic member; PA1 a laminated structure provided on a surface acoustic wave propagation path of said elastic member and comprised of at least one metal electrode and a piezoelectric member; and PA1 a means for applying an electric signal to said electrode; PA1 said elastic member having an acoustic impedance discontinuous face; PA1 said laminated structure generating a longitudinal wave upon application of the electric signal, said longitudinal wave being reflected by said acoustic impedance discontinuous face to provide a transverse wave.
In either of the methods, it is difficult to practically manufacture the desired transducer. It is especially difficult when the center frequency f.sub.0 is not high, because the lengths a and b are small. In addition, there is another problem with acoustic characteristics or aging of adhesives employed.